at one's mother's knee
US /æt wʌnz ˈmʌðərz niː/
UK /æt wʌnz ˈmʌðərz niː/

1.
from a very early age; from childhood
:
•
He learned to play the piano at his mother's knee.
•
She was taught good manners at her mother's knee.
from a very early age; from childhood